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I am presently working with Lynne Talley on the deep circulation in the Tropical Central Pacific Ocean. The analysis incorporates CTD data from WOCE Hydrographic Program sections P18, P17, and P16, along with data from the pre-WOCE TEW and EPIC hydrographic sections along 15°S and 10°N. Deep-S and buoyancy frequency signatures are used to reveal circulation patterns and allow inferences of transport magnitudes. Warm and salty tongues are found west of the East Pacific Rise Crest. Tongues are found in both hemispheres, centered about 1000 km from the equator at 2700 m. These features can be traced westward over a large fraction of the basin. They are interrupted by a cold fresh tongue about 100 km south of the equator. The cores are associated with local vertical stratification minima and are underlain by local stratification maxima. Various dynamical mechanisms that might account for these features are being explored.
Following the completion of this work, my research plans turn to a description of the bottom, deep, intermediate, and mode water circulation south of the Campbell Plateau and around the Chatham Rise. This analysis will rely heavily on recently collected CTD and hydrographic data from sections P14S and P15S. Inverse calculations south of New Zealand using P14S, P15S, and some of S4 will be used to focus on how the deep western boundary current forms against the Campbell Plateau before heading north around the Chatham Rise in the Southwest Pacific Basin. The work could be expanded to trace the boundary current's northward progress (and the southward progress of the return flow) from the Antarctic Circumpolar Current to beyond the Samoa Passage with water-mass properties (temperature, salinity, oxygen, and nutrients), stratification, and shear. This expanded analysis would benefit from the use of P6, P21, and P31 data as well as P14S and P15S data.
Another research area of interest to me is the deep and bottom water circulation in the basins east of the East Pacific Rise. The P18 section data show significant patterns in the deep and bottom water-mass properties, the stratification, and the geostrophic shear field. These signals combine to suggest sill depths, bottom water sources, and circulations for each distinct basin. I have yet to look carefully at relevant data from P19, P6, and P21, but they should reveal more about the flows in this region. This analysis of the deep and bottom water circulation in the eastern basins should synthesize measurements from P18, P19, P6, and P21. Using these data together, the circulation patterns can be described and the mass transports estimated.
Finally, inspection of CTD data from WOCE sections P18, P14S, and P15S reveals three sub-mesoscale coherent vortices (stratification minima) in the vicinity of the Antarctic Circumpolar Current. The low stratifications are centered at potential temperatures and depths of 0.8°C 3000 m, 1.3°C 2100 m, and 2.3°C 1700 m. In each instance the region of low stratification extends about 1000 m vertically. Comparisons with adjacent stations show that isopleths are deflected coherently in the vertical for 2000-3000 m, suggesting this vertical scale for the baroclinic velocity signature of the features. Interestingly, all three lenses have water-mass properties suggestive of a northern origin. Two of the features are found in the P18 data, one in the P14S data, and none in the P15S data. These features are not resolved in the horizontal, but their vertical structure can probably be used to estimate their horizontal extent. Further analysis should include a search for these features in other CTD data sets, an estimate of their density, and an assessment of their significance in effecting meridional property fluxes.
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